1. Field of Invention
This invention relates to molding of plastisol products and, in particular, to a method for in-mold indicia marking of plastisol products.
2. Brief Statement of the Prior Art
Plastisols are fluid dispersion of polyvinyl chloride resins and are used in many applications such as footwear, upholstery fabrics, shower curtains, cushions, gloves, etc. A particular application of interest is the rotationally molding of plastisols to manufacture buoys, cushioning barriers and bumpers for water craft.
Unfortunately, the surfaces of plastisol products do not readily accept conventional adhesive labels, paint or printing inks, and attempts to label, print or decorate the surfaces have not resulted in permanent bonding of labels or other indicia to the surfaces, and have lacked the capability of precise placement and resolution of indicia images.
U.S. Pat. No. 3,079,644 discloses a method for the in-mold decoration of hollow-form plastisol products. In this method, a conventional rotomolding or slush molding process is modified by introducing colored plastisol design pieces into the mold, heating the mold to a first temperature to gel the design pieces and thereafter introducing the background plastisol into the mold and heating the mold to a higher temperature to form a hollow form product in which the design pieces are incorporated in the product wall. In one embodiment of this method, design pieces are cut from a preformed and gelled, varicolored, plastisol sheet and are laid against the interior surface of the rotational mold, the background plastisol is added to the mold, and the mold is closed and heated while being rotated about two axis until a product with the desired wall thickness is formed. The patent discloses that adhesion of the gelled design pieces to the interior surface of the rotational mold can be improved by heating the mold before application of the design pieces.
While the method of this patent is useful for the decoration of large objects, it lacks the precision necessary for satisfactory application of labels and printed matter and resolution of the indicia image.